1. Field of the Invention
The present invention relates to tank vents. More specifically, this invention relates to an improvement in venting devices for use in selectively venting tanks containing liquids while preventing contaminants from entering the tank.
2. Prior Art
Venting devices for liquid tanks have long been known in the art. The simplest of these devices consists of a tube mounted on the uppermost portion of the tank wall. The tube communicates with the interior and exterior of the tank to facilitate introduction or withdrawal of liquid from the tank by allowing equalization of pressure on the contained liquid surface.
Although most venting devices are effective in equalizing the pressure within the vessel, some are not satisfactory when the tanks upon which they are mounted become other than stationary. For example, most vents satisfactorily operate only so long as the tank remains upright. Liquid tanks, such as fuel tanks and the like, may in transport be inverted allowing the fluid contained therein to escape through the vent. Such fluid loss becomes more than an economic detriment and inconvenience when the fluid being transported within the tank is flammable. The spillage or leakage of such fluids creates a fire hazard. Moreover, when the tank is a fuel tank used in a passenger vehicle such as an automobile, truck, bus, or the like, such leakage and the resulting fire hazard becomes potentially lethal to vehicle occupants. Such leakage is particularly hazardous in the aftermath of an accident.
Recently, government safety standards were promulgated which require that venting apparatus on fuel tanks used in passenger vehicles contain a means to prevent loss of fuel when the tank is overturned. To comply with these safety standards, a venting assembly has recently been developed. This assembly incorporates a spherical buoyant member, which is free to move into contact with an annular valve seat to seal the vent opening. Additionally, situated adjacent the buoyant member is a weighted member. The weighted member is free to move the buoyant member into contact with the annular valve seat by means of gravitationally forcing the buoyant member against the valve seat. Thus, the spherical surface of the buoyant member acts as a valve surface. The vent is constructed such that the weighted member is in a position to gravitationally force the buoyant member to contact the annular valve seat when the valve seat is located below the buoyant member. Such a situation normally occurs when the tank is rotated more than 90.degree. about its own axis.
Since a portion of the spherical surface of the buoyant member functions as the valve surface, the force applied by the weighted member must be distributed over a large area. If the area were smaller, the force required to sealably seat the valve surface within the annular valve seat would be less. Because of dimensional constraints within the vent chamber, the size and thus the weight of the weighted member is limited. Likewise the buoyancy of the buoyant member is limited. Therefore magnitude of the component vector applied by the weighted member upon the buoyant member is also limited. Therefore, if the tank is tilted to angles just greater than 90.degree. from vertical, the magnitude of vector force applied by the weighted member to the buoyant member can be only of a sufficient magnitude to seat the smaller valve surface.
A second disadvantage of heretofore known vent assemblies is that contaminants could gain access to the interior of the tank through the assembly. The vents communicated with the exterior of the tank by means of small orifices that become easily clogged. Further these orifices were disposed at such an angle that they become easily clogged or had to be constantly maintained. Such maintenance is expensive, and failure to so maintain a free flowing vent may result in a non-safe pressure buildup or tank collapse.